1. Field of the Invention
The present invention relates to a working oil filter device for a continuously variable transmission, for clearing the working oil circulating in the hydraulic circuit of the continuously variable transmission, of foreign substances and impurities.
2. Description of the Related Art
In a belt type continuously variable transmission (CVT) for an automobile, a drive belt made of a metal is made to run on a primary pulley mounted on a primary shaft on the drive side and having a variable pulley groove width and a secondary pulley mounted on a secondary shaft on a driven side or a follower side and having a variable pulley groove width, so that the speed of the secondary shaft may be continuously varied by varying the pulley diameters of the primary pulley and the secondary pulley hydraulically.
The speed change control of the CVT is made by controlling the oil pressures to the hydraulic cylinders disposed individually on the primary side and on the secondary side. The oil pressure to be applied to the second pulley is generated by an oil pump driven by the engine, and the secondary pressure to be applied to the hydraulic cylinder on the secondary side is reduced to adjust the primary pressure to be applied to the hydraulic cylinder on the primary side.
In order to transmit the output of the engine to the primary shaft, there is interposed between the primary shaft and the secondary shaft a forward/reverse change-over mechanism including: a forward clutch for transmitting the rotation of the crankshaft in a forward direction to the primary shaft; and a reverse brake for transmitting the same in the reverse direction. These forward clutch and reverse brake are fed with the working oil from an oil pump. In a CVT including a torque converter having a lockup clutch, on the other hand, a lockup apply chamber and a lockup release chamber are individually fed with the working oil. Moreover, the sliding portions of the CVT such as bearings or clutch facings are fed with the working oil for lubricating and cooling them so as to reduce the frictional forces and prevent the seizures.
Thus, the working oil, as discharged from the oil pump driven by the engine, is fed via the hydraulic circuit to the hydraulic cylinder for varying the pulley groove width, the clutch and the brake actuating hydraulic cylinder of the forward/reverse change-over mechanism, the individual oil chambers on the apply side and on the release side of the torque converter, and the lubricated portions. The working oil circulates between the aforementioned various oil pressure fed portions and the oil pump.
At the time of assembling the CVT, foreign substances such as cutting chips may migrate into the working oil, and worn powder may be produced at the working time of valves or from the sliding portions such as the bearings. The foreign substances or worn powder may migrate as contaminants or impurities into the working oil. With the working oil being thus contaminated, the frictional resistance is applied to the sliding portions of the valves for adjusting the oil pressure not only to become detrimental to the precise actions of the valves but also to have the valves stuck. The sliding portions may fail to be sufficiently fed with the lubricating oil thereby to lower the function of the CVT.
In order to prevent the foreign substance returned to the oil pan via the oil passage from entering the intake port of the oil pump, therefore, this oil pump is provided at its intake port with an oil strainer. If this strainer is given a fine mesh, however, a cavitation may occur in the pump when the oil has a high viscosity at a low temperature or when the speed of the oil pump is high. In order to reduce the mechanical loss of the oil pump, the intake resistance has to be lowered. Thus, the oil strainer is limited in the enhancement in the eliminating or trapping efficiency of the foreign substances.
In order to trap the foreign substances existing in the hydraulic circuit, it has been tried to assemble the oil filter in the coil passage, as disclosed in Examined Published Japanese Patent Application No. Hei. 4-69303. However, the filter assembled in the oil passage cannot be replaced, but its area has to be reduced. For the necessity for preventing the blinding of the filter, the filter is limited in its trapping efficiency so that what can be filtered out is the foreign substances of a relatively large size. If the trapping efficiency of the filter is to be improved, on the other hand, the flow resistance rises to invite the drop in the pressure or in the flow rate.
In order to trap such fine foreign obstacles as cannot be trapped by the oil strainer, it has been tried to connect a filter in series with an oil cooler, as disclosed in Unexamined Published Japanese Patent Application No. Hei 11-63175. When the working oil having been filtrated by the filter is returned to an oil pan, however, it may flow in the hydraulic circuit while entraining the fine foreign substances in the oil pan, so that the filter does not perform its function sufficiently.
Even if the ATF filter is arranged in series with the oil cooler and if the oil strainer is arranged at the intake port of the pump in the oil pan, what passes through the oil strainer is the working oil to be sucked from the oil pan by the oil pump so that what passes through the ATF filter is the working oil to flow the oil cooler. Therefore, the oil having failed to return to the oil pan circulates again in the hydraulic circuit, and the strainer may be unable to remove the foreign substances. On the other hand, the fine foreign substances, as cannot be trapped by the strainer, cannot be trapped so long as they pass through the ATF filter so that they pass through the strainer even if they return to the oil pan.
An object of the invention is to remove the foreign substances or impurities reliably from the working oil in the hydraulic circuit of a continuously variable transmission.
Another object of the invention is to keep and improve the reliability and durability of the continuously variable transmission while keeping the control performance of and preventing the reduction of the function of the continuously variable transmission.
According to a first embodiment of the invention, there is provided a working oil filter device for a continuously variable transmission including: a primary pulley mounting on a primary shaft and having a variable pulley groove width; a secondary pulley mounted on a secondary shaft having a variable pulley groove width such that a belt is made to run between said primary pulley and said secondary pulley; a forward clutch for transmitting the output of an engine in a forward direction to said primary shaft; and a reverse brake for transmitting the same in a reverse direction to said primary shaft. The filter device comprises: a secondary pressure adjust valve for adjusting and feeding the working oil, as discharged by an oil pump driven by said engine, to a secondary cylinder for varying the pulley groove width of said secondary pulley; a clutch pressure adjust valve disposed in a clutch pressure passage connecting the drain port of said secondary pressure adjust valve, said forward clutch and said reverse brake, for adjusting a clutch pressure from an original pressure or the drain pressure of said secondary pressure adjust valve; a lubrication pressure adjust valve disposed in a lubrication pressure passage connecting the drain port of said clutch pressure adjust valve and a lubricated portion, for adjusting a lubrication pressure with setting the drain pressure of said clutch pressure adjust valve to an original pressure; and a filter disposed on the upstream side of said clutch pressure passage.
According to a second embodiment of the invention, there is provided a working oil filter device for a continuously variable transmission including: a primary pulley mounting on a primary shaft and having a variable pulley groove width; a secondary pulley mounted on a secondary shaft having a variable pulley groove width such that a belt is made to run between said primary pulley and said secondary pulley; a forward clutch for transmitting the output of an engine in a forward direction to said primary shaft; and a reverse brake for transmitting the same in a reverse direction to said primary shaft. The filter device comprises: a primary pressure adjust valve for adjusting and feeding the working oil, as discharged by an oil pump driven by said engine, to a primary cylinder for varying the pulley groove width of said primary pulley; a secondary pressure adjust valve for adjusting and feeding the working oil, as discharged by said oil pump, to a secondary cylinder for varying the pulley groove width of said secondary pulley; and a filter disposed in a line pressure passage for guiding the discharge port of said oil pump, said primary pressure adjust valve and said secondary pressure adjust valve.
According to the first and second embodiments of the invention, the working oil filter device for the continuously variable transmission comprises: a check valve disposed in a bypass passage connecting the upstream side and the downstream side of said filter, for guiding the working oil to the downstream side when the oil pressure on the upstream side is higher than that on the downstream side by a predetermined value or higher.
According to a third embodiment of the invention, there is provided a working oil filter device for a continuously variable transmission including: a primary pulley mounting on a primary shaft and having a variable pulley groove width; a secondary pulley mounted on a secondary shaft having a variable pulley groove width such that a belt is made to run between said primary pulley and said secondary pulley; a forward clutch for transmitting the output of an engine in a forward direction to said primary shaft; and a reverse brake for transmitting the same in a reverse direction to said primary shaft. The filter device comprises: a secondary pressure adjust valve for adjusting and feeding the working oil, as discharged by an oil pump, to a secondary cylinder for varying the pulley groove width of said secondary pulley; a lubrication pressure adjust valve disposed in a lubrication pressure passage connecting the drain port of said secondary pressure adjust valve and a lubricated portion for adjusting a lubrication pressure with setting the drain pressure of said secondary pressure adjust valve to an original pressure; a filter disposed in a drain oil passage connecting the drain portion of said lubrication pressure adjust valve and the intake port of said oil pump; and a bypass passage for providing the communication between a bypass port disposed in said lubrication pressure adjust valve and adapted to be opened, when the amount of the working oil to be fed to said filter increases, and the downstream side of said filter.
According to another aspect of the third embodiment of the invention, there is provided a working oil filter device for a continuously variable transmission including: a primary pulley mounting on a primary shaft and having a variable pulley groove width; a secondary pulley mounted on a secondary shaft having a variable pulley groove width such that a belt is made to run between said primary pulley and said secondary pulley; a forward clutch for transmitting the output of an engine in a forward direction to said primary shaft; and a reverse brake for transmitting the same in a reverse direction to said primary shaft. The filter device comprises: a secondary pressure adjust valve for adjusting and feeding the working oil, as discharged by an oil pump, to a secondary cylinder for varying the pulley groove width of said secondary pulley; a lubrication pressure adjust valve disposed in a lubrication pressure passage connecting the drain port of said secondary pressure adjust valve and a lubricated portion for adjusting a lubrication pressure with setting the drain pressure of said secondary pressure adjust valve to an original pressure; a filter disposed in a drain oil passage connecting the drain portion of said lubrication pressure adjust valve and the intake port of said oil pump; and a drain pressure adjust valve disposed in a bypass passage connecting the upstream side and the downstream side of said filter, for opening said bypass oil passage when the amount of the working oil fed to said filter increases.
According to the first and third embodiments of the invention, in the working oil filter device for the continuously variable transmission, the filter is removably mounted on a casing covering a member constructing the continuously variable transmission.
According to the second embodiment of the invention, in the working oil filter device for the continuously variable transmission, the filter includes: a filter casing formed integrally with a casing covering members constructing the continuously variable transmission; and a filter element mounted removably in said filter casing.